Method and apparatus for plugging perforations

ABSTRACT

Apparatus and method for plugging perforations in an oil or gas well. A bridge plug is formed in the casing below the perforations. A heating tool and a fusible alloy adjacent the heating tool is lowered into the well to a position above the bridge plug and adjacent the perforations. Heat is applied to melt the fusible alloy and pressure is applied to the molten material to force it through the perforations. The heating operation is terminated to allow the molten material to solidify and plug the perforations.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application Ser. No. 60/805,734 filed Jun. 24, 2006 entitled PERFORATION PLUGGING TOOL AND PROCEDURE (Spencer).

INTRODUCTION

This invention relates to method and apparatus for plugging perforations in an oil or gas well and, more particularly, to plugging an oil or gas well which utilizes a fusible alloy for plugging the perforations.

BACKGROUND OF THE INVENTION

In the oil and gas production industry, a perforated interval in the casing of the well is created to allow enhanced oil flow from the oil holding formation into the casing. The perforations are holes that extend from the inside of the well casing to the outside and are created by explosive shooting or other perforation techniques which techniques form no part of the present invention.

Following the long use of the perforations for oil or gas flow into the casing, water flow becomes a problem. The water is undesirable since it mixes with the oil and must be removed from the oil at the surface. Furthermore, when water increases its flow through the perforations, the oil or gas flow may diminish to a point where the well is not longer commercially viable. In addition, the water flow may hinder the recovery of oil or gas from other areas of the formation. It therefore becomes advantageous to plug the previously formed perforations.

In our earlier U.S. Pat. No. 6,828,531, the contents of which are incorporated herein by reference, there is disclosed a method and apparatus for plugging perforations using a squeeze procedure and a heating tool that melts a fusible alloy and squeezes the alloy into the perforations where the alloy cools and expands thereby closing the perforations and terminating flow therethrough. The use of such a technique, while useful to close the perforations, also results in an residue of alloy being left within the well as a solid alloy plug across the casing. The cost of the alloy to effect plugging in such an application is expensive. Further, the time to create the plugging in that application is unnecessarily time consuming.

It would advantageous to use less alloy for plugging the perforations and it further would be advantageous to enhance the efficiency of the plugging operation.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a heating tool for use in plugging perforations in an oil or gas well comprising a heating element, a circumferential tube surrounding said heating element, a fusible alloy adjacent to and outside said circumferential tube and means for releasably connecting said circumferential tube and said fusible alloy to said heating element.

According to a further aspect of the invention, there is provided a method of plugging perforations in the casing of an oil or gas well comprising the steps of forming a bridge plug in said casing at a position lower than the lowermost perforation sought to be plugged, lowering a heating tool and a fusible metal alloy to a position above said bridge plug and adjacent said perforations sought to be plugged, melting said alloy and applying pressure to said molten alloy to force said molten alloy through said perforations in said casing, lowering the temperature of said heating tool to allow said molten alloy to solidify within said perforations, removing said pressure from said molten alloy and withdrawing said heating tool from said oil or gas well.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

An embodiment of the invention will now be described, by way of example only, with the use of drawings in which:

FIG. 1 is a diagrammatic cross-sectional illustration of an oil or gas well illustrating a perforated interval within the casing of an oil or gas well;

FIG. 2 is a diagrammatic cross-sectional view of the oil or gas well of FIG. 1 and illustrating the initial step of forming a bridge plug in the well to plug the well and a sand pad interval formed on the top of the bridge plug;

FIG. 3 is a diagrammatic cross-sectional view of the oil or gas well of FIGS. 1 and 2 and further illustrating a heating tool lowered into the well by way of electrical line cable together with the fusible alloy material located on the outside of the tool;

FIG. 4 is a diagrammatic cross-sectional view similar to FIG. 3 but illustrating pressure being applied on the molten alloy material thereby to force the alloy through the perforations; and

FIG. 5 is a diagrammatic cross-sectional view of the well of FIGS. 1-4 but illustrating the solidified alloy within the perforations and with the heating tool having been removed from the well.

DESCRIPTION OF SPECIFIC EMBODIMENT

Referring now to the drawings, an oil or gas well is generally illustrated at 10 in FIG. 1 with the production casing 11 being cemented in by cement 12 which seals the production casing from the formation of interest which is an oil or gas bearing formation generally illustrated at 13.

Perforations 14 have been formed in the casing 11 and extend into the formation of interest 13.

It is desired to plug the perforations 14 and to terminate flow from the formation 13 through the perforations 14 and into the casing 11. To do so, a retrievable bridge plug 21 is set in the casing 11 below the lowest one of the perforations 14 as illustrated in FIG. 2. The bridge plug 21 is formed within the casing 11 using wire line procedure which is known. A volume of sand 22 is then dumped into the casing 11 and on top of the bridge plug 21. The thickness of the sand layer 22 should extend upwardly to a position just below the lowermost one of the perforations of interest 14.

Referring to FIG. 3, a heating and perforation plugging tool generally illustrated at 23 is lowered into the well 10 by electrical wire line cable 24 until it rests on the sand layer 22. Tool 23 is an electrical resistance type heater which has a heating coil diagrammatically illustrated at 30 which is connected to an electrical power supply (not shown) at the surface through electrical cable 24. A tube 30 is positioned outside the heating coil 31 and terminates at the lower end of the tool 23 with a flanged cap 32. The tube 30 is conveniently made from a relatively soft metal with high thermal conductivity such as aluminum although copper or brass or other metals are also contemplated to be useful. A latching mechanism generally illustrated at 33 maintains the tube 30 and flanged cap 32 in position relative to the heating coil 31 as will be described.

The layer 34 of meltable fusible alloy is formed around the circumference of the tube 30 and is in solid form as the heating tool 23 is lowered from the surface. The fusible alloy 34 is conveniently a bismuth/tin alloy although other such suitable alloys are also contemplated. The volume of the alloy 34 surrounding the tube 30 is earlier calculated and is such that the perforations 14 will be completely filled when the alloy 34 is melted.

Referring to FIG. 4, electric power is applied to the heating coil 30 through the electrical wire line cable 24. The heat is transmitted though the aluminum tube 31 and melts the fusible alloy material 34. Simultaneously with the melting of the alloy 34, pressure is applied to the melted alloy 34 by pumped water or by a compressed gas. The pressure forces the molten alloy 34 into the perforations 14 extending through the casing 11 and the cement 12 and into the formation 20.

Power to the heating tool 23 is then terminated and the latching mechanism 33 opens thereby allowing the tube 31 and flanged cap 32 to be released from the heating tool 23 where they remain on the bridge plug 21 and sand 22. The pressure remains on the molten alloy and the cessation of heating from the tool 23 causes the molten alloy 34 to solidify within the perforations 14. The bismuth/tin alloy 34 expands as it solidifies thereby creating a tight plug within the perforations 14 and blocking the entrance of the undesired water into the well 10. Following a sufficient time interval, the pressure on the alloy 34 within the well 10 is terminated and the heating tool 23 is withdrawn from the well 10. Any alloy remaining within the casing 11 is readily drilled out. The bridge plug 21 and sand 22 are likewise removed as is known. The solidified alloy 34 will remain in the perforations 14 thereby plugging the perforations 14.

Many modifications will readily occur to those skilled in the art to which the invention relates. It is desirable to have the tube 31 and solid alloy 34 brought into close proximity with the inside diameter of the casing 11 in order to enhance movement of the melted alloy into the perforations 14 and also to minimize the amount of alloy required for plugging the perforations 14. Accordingly, tubing 34 of various diameters could be accommodated by the heating tool 23. Likewise, while a latching mechanism 30 has been described, other mechanisms for allowing the release of the tubing 30 and alloy 34 such as shear pins, molded fusible metal which melts under the influence of heat from the heating tool 23 contemporaneously with the melting of the fusible alloy 34 used for plugging the perforations, and the like are likewise contemplated.

The alloy material 34 on the outside of the releasable tube of the heating tool 23 as is described and illustrated may be formed on the outside of the tube 31 or it may conveniently be pre-molded in segments which segments would be slipped over the tube 31 in the desired quantities. The segments would then rest against the flanged cap 32 but the operation of the heating tool 23 would be similar to the operation just described.

While a resistive type heating tool 23 has been described, it is contemplated that an inductive type heating tool such as that heating tool described in our U.S. Pat. No. 6,825,531 would also be useful. There would be no need for a hollow center in such a tool but the use of induction for heating the fusible alloy 34 is contemplated to be useful for the present application.

Many further embodiments will readily occur to those skilled in the art to which the invention relates and the specific embodiments described should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims. 

1. A heating tool for use in plugging perforations in an oil or gas well, said tool comprising a heating element, a circumferential tube surrounding said heating element, a fusible alloy adjacent to and outside said circumferential tube and means for releasably connecting said circumferential tube and said fusible alloy to said heating element.
 2. A heating tool as in claim 1 wherein said circumferential tube is a thermally conductive metal material.
 3. A heating tool as in claim 2 wherein said fusible alloy is formed around said heating tube.
 4. A heating tool as in claim 1 wherein said means for releasably connecting said circumferential tube and said fusible alloy to said heating element is a latching means which in its closed position retains said tube and which opens to release said circumferential tube and said fusible alloy.
 5. A heating tool as in claim 2 wherein said fusible alloy is formed in segments which are mounted around said circumferential tube.
 6. Method of plugging perforations in the casing of an oil or gas well comprising the steps of forming a bridge plug in said casing at a position lower than the lowermost perforation sought to be plugged, lowering a heating tool and a fusible metal alloy to a position above said bridge plug and adjacent said perforations sought to be plugged, melting said alloy and applying pressure to said molten alloy to force said molten alloy through said perforations in said casing, lowering the temperature of said heating tool to allow said molten alloy to solidify within said perforations, removing said pressure from said molten alloy and withdrawing said heating tool from said oil or gas well.
 7. Method as in claim 6 wherein said fusible alloy surrounds said heating tool.
 8. Method as in claim 7 wherein said fusible alloy is formed on the circumference of said heating tool.
 9. Method as in claim 7 wherein said fusible alloy is formed in segments and said segments are fitted around said heating tool.
 10. Method as in claim 9 wherein the quantity of fusible alloy surrounding said heating is sufficient to fill said perforations in said oil or gas well.
 11. Method as in claim 10 wherein said fusible alloy is a bismuth-tin alloy.
 12. Method as in claim 11 wherein said heating tool further comprises a heating tube and said fusible alloy extends around the circumference of said heating tube.
 13. Method as in claim 12 wherein said heating tube is made from aluminum.
 14. Method as in claim 13 wherein said heating tool is a resistive type heating tool.
 15. Method as in claim 13 wherein said heating tool is an inductive type heating tool.
 16. Method as in claim 6 and further comprising depositing a layer of sand on top of said bridge plug. 